1. Field of the Invention
The present invention relates to a method of forming a conductor layer through a vapor growth (deposition) process, and more particularly to a method of selectively forming a silicon-containing metal layer to fill a contact hole for a silicon substrate or a conductor layer of, for example, aluminum of a semiconductor device, or to cover a conductor layer in a semiconductor device.
2. Description of Related Art
Recently, the number of components for a semiconductor device such as an LSI has increased and the dimensions of the device have been reduced. The filling of contact holes, reliability of conductor layers (interconnections), low resistance contact to a silicon substrate, barrier metal formation, etc., all require improvement: For example, the miniaturization of a conductor (interconnection) pattern is accompanied by a decrease in contact hole dimensions, and when a conductor layer is formed to come into contact with a silicon substrate through such a small contact hole, step coverage of the conductor layer becomes poor. To solve these step coverage problems, the contact hole is filled with a refractory metal such as tungsten (W), which is selectively deposited therein by vapor phase deposition (growth), and the conductor layer is formed over the filler (i.e., refractory metal layer) to electrically connect with the silicon substrate through the filler. The selective deposition of W is carried out by using a reaction gas mixture of a WF.sub.6 gas and a H.sub.2 gas at a temperature of 400.degree. C. or more to obtain a practical deposition rate. A proposal was made in which tungsten silicide is selectively deposited by using a silane (SiH.sub.4) gas instead of the H.sub.2 gas (Japanese Unexamined Patent Publication (Kokai) No. 59-72132, published on Apr. 24, 1984). In an example of Japanese Publication No. 59-72132, a contact hole is filled with a tungsten layer in a low pressure CVD (chemical vapor deposition) reactor under the conditions of flow rates of a WF.sub.6 gas, a SiH.sub.4 gas and an argon (Ar) gas of 1 cc/min, 3 cc/min and 1000 cc/min, respectively, an inside pressure of the reactor of 0.2 Torr, and a substrate temperature of 450.degree. C.
A method of depositing metal silicide such as molybdenum silicide and tungsten silicide (MSi.sub.x : M indicates metal, 1.7.ltoreq.x.ltoreq.2.3) by low-pressure vapor phase deposition is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 62-267472 (published on Nov. 20, 1987, later than the first priority date of the present application, and corresponding to U.S. Ser. No. 863,622). In this case, in Example 1 for example, a flow rate of a SiH.sub.4 gas is 5-27 times as large as that of a MoF.sub.6 gas and a blanket deposition instead of a selective deposition occurs. U.S. Pat. No. 4,684,542 discloses that tungsten silicide (WSi.sub.x : 2.2.ltoreq.x.ltoreq.3.4, FIG. 5) is vapor phase deposited on a substrate by using a WF.sub.6 gas and a higher order silane gas (Si.sub.n H.sub.2n+2, n=2, 3, . . . ). In this case, a flow rate of the high order silane gas is larger than that of the WF.sub.6 gas, and a blanket deposition instead of the selective deposition occurs.
In the selective deposition of tungsten using the WF.sub.6 gas and the H.sub.2 gas, an encroachment or a worm hole in a silicon substrate occurs and increases the junction leakage in a semiconductor device.
When the selective deposition is made using a SiH.sub.4 gas instead of an H.sub.2 gas, the deposition temperature is still relatively high, and a method of selective deposition at a lower temperature is required.
The miniaturization and a greater integration of a semiconductor device are accompanied by a decrease in the width and thickness of a conductor layer of aluminum (Al) or aluminum alloy (Al alloy). Consequently, the generation of metal voids or hillocks, and the generation of stress migration due to thermal stress and interlaminar stress and/or the generation of electromigration due to an increase of the current density, increase open circuit failures of the conductor layers. To decrease the open circuit failures, attempts have been made in which copper (Cu) and/or titanium (Ti) are added into Al (or Al alloy) of the conductor layer, the stress of a laminated layer is decreased, and a tungsten layer is selectively formed on a surface of the conductor layer only. Such a selective formation of tungsten is carried out by a vapor phase deposition due to a chemical reaction of a WF.sub.6 gas and a SiH.sub.4 gas. In general a selective or blanket deposition (growth) of tungsten or tungsten silicide is carried out at a relatively high temperature of 300.degree. C. or more, but as miniaturization is increased, the influence of thermal stress due to a formation process (e.g., increase of stressmigration) can not be ignored, and as a result, a lower temperature process (if possible, a formation process at room temperature) is required.